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Full text of "Text Book Of Mechanical Engineering"

790

Appendix 1L

ROSEBANK, SCOTLAND.
(Strong foundry iron.)


	Comb. C.
	Si.
	P.
	S.
	Mn.

Percentages
	•46
	1-31
	'53
	-06
	'99

JP. So. Spiegeleisen owes its value mostly to the presence
of manganese, which varies from 3\ to 11£% at different times,
but less than 6% renders the material useless for steel making.
There is also about 5% of combined carbon, and the fracture
shews large crystals. Probably, too, the silicon present is of use,
for both manganese and silicon generally improve the quality of
steel.

P. 82. Whitworth Compressed SteeL—Apparently the
existence of blowholes in steel ingots is due to the fact that low-
carbon steel, when molten, is capable of occluding or holding in
solution certain gases. When solidification sets in, these gases
are liberated from the fluid only to be immediately imprisoned
by the solidifying steel, while slower cooling only increases
sponginess, for then rnore gases are given off. To avoid the loss
occasioned by the cutting away of the ingot head, and to improve
the rest of the metal, three principal methods are in vogue :

(1)  Chemical treatment {addition of silicon or manganese}.

(2)  Forging or Cogging {under steam hammer or hydraulic press}.

(3)  Compression           {when fliiid}.

Silicon and manganese diminish the gas released, and collect
such bubbles as are already formed, but they reduce ductility.

In the Whitworth process, a powerful hydraulic press is
applied to the molten steel when in the ingot mould, producing
a thoroughly sound material by the elimination of all bubbles.
The press is shewn in Fig. 766. The fixed head H rests on four
screwed columns DD, which are again supported oh the base-
casting A. The pressure water is admitted tinder ram B, which